STEERING SYSTEM
In automobiles, steering wheel, gears, linkages, and other components are
used to control the direction of a vehicleâ&#x20AC;&#x2122;s motion. Failure to any of these
components will lead to fatal accidents.
Steering system helps the student to understand the different types of
steering systems ,its working, the operating principle of hydraulic power
steering systems, MDPS (Motor Driven Power Steering ) and to service and
diagnose these systems.

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ACKERMANN STEERING GEOMETRY
Ackermann steering geometry is a geometric arrangement of linkages in the steering of a car
or other vehicle designed to solve the problem of wheels on the inside and outside of a turn

Ackermann geometry
needing to trace out circles of different radius. It was invented by the German Carriage Builder
Georg Lankensperger in Munich in 1817, then patented by his agent in England, Rudolph
Ackermann (1764–1834) in 1818 for horse drawn carriages.
The intention of Ackermann geometry is to avoid the need for tyres to slip sideways when
following the path around a curve. The geometrical solution to this is for all wheels to have
their axles arranged as radii of a circle with a common centre point. As the rear wheels are
fixed, this centre point must be on a line extended from the rear axle. Intersecting the axes
of the front wheels on this line as well requires that the inside front wheel is turned, when
steering, through a greater angle than the outside wheel.
Rather than the preceding “turntable” steering, where both front wheels turned around a
common pivot, each wheel gained its own pivot, close to its own hub. While more complex,
this arrangement enhances controllability by avoiding large inputs from road surface variations
being applied to the end of a long lever arm, as well as greatly reducing the fore-and-aft
travel of the steered wheels. A linkage between these hubs moved the two wheels together,
and by careful arrangement of the linkage dimensions the Ackermann geometry could be
approximated. This was achieved by making the linkage not a simple parallelogram, but by
making the length of the track rod (the moving link between the hubs) shorter than that of
the axle, so that the steering arms of the hubs appeared to “toe out”. As the steering moved,
the wheels turned according to Ackermann, with the inner wheel turning further. If the track
rod is placed ahead of the axle, it should instead be longer in comparison, thus preserving this
same “toe out”.
Simple approximation for designing Ackermann geometry

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A simple approximation to perfect Ackermann steering geometry may be generated by moving
the steering pivot points inward so as to lie on a line drawn between the steering kingpins and
the centre of the rear axle. The steering pivot points are joined by a rigid bar called the tie rod
which can also be part of the steering mechanism, in the form of a rack and pinion for instance.
With perfect Ackermann, at any angle of steering, the centre point of all of the circles traced
by all wheels will lie at a common point. Note that this may be difficult to arrange in practice
with simple linkages, and designers are advised to draw or analyze their steering systems over
the full range of steering angles.
Modern cars do not use pure Ackermann steering, partly because it ignores important dynamic
and compliant effects, but the principle is sound for low speed manoeuvres. Some race cars
use reverse Ackermann geometry to compensate for the large difference in slip angle between
the inner and outer front tyres while cornering at high speed. The use of such geometry helps
reduce tyre temperatures during high-speed cornering but compromises performance in low
speed maneuvers.

INTRODUCTION
In automobiles, steering wheel, gears, linkages, and other components are used to control
the direction of a vehicleâ&#x20AC;&#x2122;s motion. Because of friction between the front tires and the road,
especially in parking, effort is required to turn the steering wheel. To lessen the effort required,
the wheel is connected through a system of gears to components that position the front tires.
The gears give the driver a mechanical advantage, i.e., they multiply the force he applies.

COMPONENTS OF STEERING SYSTEM.
According to the type of steering gear box using the components of the steering system are
varies.
In modern days mainly two types of steering systems are mainly using.They are rack and pinion

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steering system and recirculating ball type steering system.There is also worm and nut worm
and sector steering gear boxes are also using.

A rack-and-pinion gear set is enclosed in a metal tube, with each end of the rack protruding
from the tube. A rod, called a tie rod, connects to each end of the rack. The pinion gear is
attached to the steering shaft. When you turn the steering wheel, the gear spins, moving the
rack. The tie rod at each end of the rack connects to the steering arm on the spindle. The rackand-pinion gear set converts the rotational motion of the steering wheel into the linear motion
needed to turn the wheels and provides a gear reduction, making it easier to turn the wheels.
The pinion gear is attached to the steering shaft. When you turn the steering wheel, the gear
spins, moving the rack. The tie rod at each end of the rack connects to the steering arm on the
spindle
The rack-and-pinion gear set does two things:
• It converts the rotational motion of the steering wheel into the linear motion needed
to turn the wheels.
• It provides a gear reduction, making it easier to turn the wheels.
On most cars, it takes three to four complete revolutions of the steering wheel to make the
wheels turn from lock to lock (from far left to far right).
The steering ratio is the ratio of how far you turn the steering wheel to how far the wheels
turn. For instance, if one complete revolution (360 degrees) of the steering wheel results in
the wheels of the car turning 20 degrees, then the steering ratio is 360 divided by 20, or 18:1.

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A higher ratio means that you have to turn the steering wheel more to get the wheels to turn
a given distance. However, less effort is required because of the higher gear ratio.
Generally, lighter, sportier cars have lower steering ratios than larger cars and trucks. The
lower ratio gives the steering a quicker response -- you donâ&#x20AC;&#x2122;t have to turn the steering wheel
as much to get the wheels to turn a given distance -- which is a desirable trait in sports cars.
These smaller cars are light enough that even with the lower ratio, the effort required to turn
the steering wheel is not excessive.
Some cars have variable-ratio steering, which uses a rack-and-pinion gear set that has a
different tooth pitch (number of teeth per inch) in the center than it has on the outside. This
makes the car respond quickly when starting a turn (the rack is near the center), and also
reduces effort near the wheelâ&#x20AC;&#x2122;s turning limits.

RECIRCULATING BALL TYPE STEERING GEAR BOX

Construction
Recirculating ball, also known as recirculating ball and nut is a steering mechanism commonly
found in older automobiles, and some trucks.
The recirculating ball steering mechanism contains a worm gear inside a block with a threaded
hole in it; this block has gear teeth cut into the outside to engage the sector shaft (also called
a sector gear) which moves the Pitman arm. The steering wheel connects to a shaft, which
rotates the worm gear inside of the block. Instead of twisting further into the block, the worm
gear is fixed so that when it spins, it moves the block, which transmits the motion through the
gear to the pitman arm, causing the road wheels to turn.
The worm gear is similar in design to a ball screw; the threads are filled with ball bearings that
recirculate through the gear and rack as it turns. The balls serve to reduce friction and wear in
the gear, and reduce slop. Slop, when the gears come out of contact with each other, would be
felt when changing the direction of the steering wheel, causing the wheel to feel loose

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Working
This is how mechanical steering, “worm and sector recirculating ball steering”, works. Any
rotation of the steering wheel is transferred via the steering column to a steering worm. The
steering worm is - in simple terms - rather like a screw with a thread. The counterpart to the
screw is formed by the nut - here called the steering gear nut. As a link between the steering
worm and the steering gear nut, steel balls are embedded in the thread, and these help to
reduce friction during the turning motion. The steering worm and steering gear nut have, as it
were, a thread with ball bearings. The steering gear nut is so fixed that is can not move “right
round” during the turning process
When the steering wheel is turned, the steering gear nut moves along the steering worm.
The steering gear nut has a row of teeth on one side meshed directly with the sector on the
Pitman shaft . All movements of the shaft are transferred to the wheels via the drop arm and
the steering linkage.
The advantages of worm and sector recirculating ball steering are based on two points. First
of all, there is very little friction between the steering worm and steering gear nut due to
the system of “recirculating balls”, thus making for light, positive steering. Furthermore, such
steering has a constant reduction ratio within the steering box.

Adjustment
Correctly adjusted worm bearings have no clearance and no pre-load. The Pitman shaft
adjusting screw must be adjusted when the steering wheel is in the straight ahead position;
tighten the adjusting screw until the spring is fully compressed and then back off approximately
3-4mm, measured at the circumference of the adjusting screw.
The main components of steering system are tie rod, tie rod end, pitman arm, steering column,
and steering wheel.

Recirculating
Ball Gearbox

Tie
Rod

Track
Rod

Pitman
Arm

Steering Arms

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Tie
Rod

Pitman Arm
STEERING SHAFT

CAM

HOUSING

CROSS SHAFT

STUDS

LEVER

BALL CUP BALLS
PITMAN ARM

The Pitman arm is a linkage attached to the steering gear sector shaft, that converts the angular
motion of the sector shaft into the linear motion needed to steer the wheels. The Pitman arm
is supported by the sector shaft and supports the drag link or center link with a ball joint. It
transmits the motion it receives from the steering box into the drag (or center) link, causing it
to move left or right to turn the wheels in the appropriate direction. The idler arm is attached
between the opposite side of the center link from the Pitman arm and the vehicleâ&#x20AC;&#x2122;s frame
to hold the center or drag link at the proper height. A worn ball joint can cause play in the
steering, and may get worse over time.

Tie Rod
Tie-Rod Assemblies Two tie-rod assemblies are used to fasten the center link to the
steering knuckles. Ball sockets are used on both ends of the tie-rod assembly. An adjustment
sleeve connects the inner and outer tie rods. These sleeves are tubular in design and threaded
over the inner and outer tie rods. The adjusting sleeves provide a location for toe adjustment.
Clamps and clamp bolts are used to secure the sleeve. Some manufacturers require the
clamps be placed in a certain position in relation to the tie rod top or front surface to prevent
interference with other components.

Ball sockets
Ball sockets are like small ball joints; they provide for motion in all directions between two
connected components. Ball sockets are needed so the steering linkage is NOT damaged or
bent when the wheels turn or move up and down over rough roads. Ball sockets are filled
with grease to reduce friction and wear. Some have a grease fitting that allows
chassis grease to be inserted with a grease gun. Others are sealed by the manufacturer and
cannot be serviced

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Steering Column
Steering column assembly

Intermediate shaft

Power-assisted steering system

Universal joint

Steering column

The steering column assembly is bolted to the bulkhead. The steering column shaft is mounted
in two needle bearings suspended in rubber mountings in the steering column assembly. A
jointed intermediate shaft connects the steering column to the steering gear. For reasons
of safety the steering column assembly incorporates a collapsible steel cage, a telescopic
steering column shaft and an intermediate shaft with a deformation zone designed to crumple
progressively in the event of a head-on collision. In addition, the joint configuration is such
that the shaft will be directed away from the driver in a collision. Adjustment of the position of
the steering wheel spokes is achieved by adjusting the toe-in on both sides of the car.

Steering Wheel
The steering wheel is the part of the steering
system that is manipulated by the driver; the rest
of the steering system responds to such driver
inputs. This can be through direct mechanical
contact as in recirculating ball or rack and pinion
steering gears, without or with the assistance of
hydraulic power steering.

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HYDRAULIC POWER STEERING.
Introduction
Power steering helps drivers steer vehicles by augmenting steering effort of the steering
wheel. It does this by adding controlled energy to the steering mechanism, so the driver needs
to provide only modest effort regardless of conditions. In particular, power steering helps
considerably when a vehicle is stopped or moving slowly.
The hydraulic power steering system uses a hydraulic pressure which is generated by the power
steering pump to reduce the effort required to turn the steering wheel. The power steering
pump is mounted on the front of the engine. The pump is driven by the crankshaft through a
drive belt.
Power steering uses hydraulic pressure for reduction of steering effort, enabling the driver to
easily operate the steering wheel. Steering effort is generally 20N to 39N. In addition to that,
power steering systems offer higher stability during driving and prevention of shock from road
surface irregularities that may otherwise be transmitted to the steering wheel.

Rack and pinion steering gear box
The cylinder is part of the steering gear housing. The rack is equipped with a piston complete
with seals. For the flow of power steering fluid to and from the control valve there are two
connections on the servo cylinder, one on each side of the piston. When turning right, power
steering fluid is pumped to the right hand section of the servo cylinder. Piston and rack are
forced to the left and power steering fluid is discharged from the left hand section of the servo
cylinder. The rubber gaiter on the left hand side is distended at the same time as the one on
the right side is compressed. Movement of the rack is transferred via the inner ball joints (3.),
track rod and outer track rod ends to the steering arms of the steering swivel member. Both
the inner ball joints and the outer track rod ends are lubricated for life and self-adjusting, with
no further lubrication or adjustment being necessary or possible.

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Oil Pump
Vane
Cam ring

Cover
Rotor

Pully
Oil seal

O-ring

O-ring

Flow control valve

The hydraulic power for the steering is provided by a rotary-vane pump. This pump is driven
by the carâ&#x20AC;&#x2122;s engine via a belt and pulley. The pump element consists of a rotor with a number
of slits, a vane for each slit, a pump ring and two end plates with inlet and outlet ports for
power steering fluid. Due to the oval shape of the pump ring, the volume between the vanes
increases and decreases twice during each revolution of the rotor. Inlet ports lead to the areas
in which the volume increases and outlet ports lead from those in which the volume decreases,
thereby producing a pumping effect. Apart from being forced outwards by centrifugal force,
the vanes are also pressed outwards against the pump ring by the pressure of the fluid. The
fluid is directed into the slots inside the vanes.

Pressure and Flow Control Valve

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The purpose of the control valve is to regulate the flow from the pump so that it remains
constant, regardless of engine/pump rpm. The control valve sits on one side, directly connected
to the pump flow . At the outlet passage of the pump, a restrictor is situated from which a
connecting passage leads to the other side of the valve, which contains a spring .When not
actuated, the valve presses against the outlet side. When pressure is high, an overflow valve
housed in the control valve is actuated by the power steering fluid pressure on the spring
loaded control valve. For the control valve to operate, a certain amount of power steering fluid
must circulate through it continuously ,although not when the steering wheel is at full lock.
Steering and parking at low engine speed

The pressure produced by the pump is slightly reduced over the restrictor at the pump outlet.
The reduced pressure is led to the spring loaded side of the control valve, at which time there
is a minor pressure difference between the two sides of the valve. Due to the low pump speed,
however, this pressure difference is not enough to actuate the valve.
Steering at high engine speed (pump in flow control mode)

The flow of power steering fluid inside the pump increases with increasing engine rpm and
owing to the restrictor in the pump outlet the flow velocity also increases. This reduces the
pressure in the connecting passage, with the result that the pressure on the spring loaded side
of the control valve will be lower than that acting on the outlet side of the valve. The valve
therefore overcomes the force of the spring, opening a port to the suction side of the pump

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and allowing a certain amount of internal recirculation of the fluid to take place so that the
flow from the pump is maintained at constant rate, regardless of engine /pump rpm.
Steering wheel turned to full lock

Pump speed in this case is often low. When the steering wheel is turned to full lock, the
control valve of the steering gear closes. The flow of fluid from the pump will then be zero. The
resulting high pressure is directed via the connection passage to the spring loaded side of the
control valve. The pressure opens the overflow valve and allows the fluid to pass to the inlet
side of the pump. The pressure difference across the control valve forces it to move against
the spring and thus open the port for recirculation of the full delivery flow from the pump. The
predetermined maximum pressure is maintained as long as the control valve remains closed.

Hydraulic Control Valve
The hydraulic control valve consists of a valve
spool (1.), a sleeve (2.) , a torsion bar (3.) and a
pinion (4.). The steering columnâ&#x20AC;&#x2122;s intermediate
shaft is connected to the valve by means of a
universal joint. The torsion bar is connected to
the upper end of the valve by means of a pin
(5.). The other end of the torsion bar is press
fit in the pinion. The sleeve is connected to the
pinion by a pin (6.) and follows the rotation
of the pinion exactly. There is also a fail safe
connection between the valve spool and the
pinion required to maintain steer ability in
case the torsion bar is broken. The sleeve has
three radial grooves (7.), the power steering
fluid being pumped to the middle one. When
the steering wheel is in straight ahead position,
the control valve is open and the fluid flows
up through the valve and back to the power
steering reservoir via the chamber above the
sleeve. The upper end of the pinion is mounted
in a needle bearing while the lower end is
mounted in a ball bearing. A spring loaded
plunger presses the rack against the pinion.

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When the steering wheel is turned, the movement is transferred via the torsion bar to the
pinion. Since the torsion bar is somewhat elastic, there will be a difference between the
degree of rotation of the valve spool (which follows the rotation of the intermediate shaft)
and the sleeve which is fixed to the pinion. As a result, the fluid can no longer flow through
the control valve and back to the power steering fluid reservoir directly. Instead, delivery and
return passages open for the servo cylinder.

Operating Principle

Input shaft Torisioning bar

Rotary valve

In straight ahead position.

Pressurized oil is delivered through port „a“ and to the right (port b) and left (port „c) servo
cylinder. The pressure in both, the left and right servo cylinders are equal, and the oil is drained
through the open port „d“ back to the reservoir.

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When turning left

Power steering fluid is pumped to the left hand side of the servo cylinder via the upper radial
groove (port „b“) of the sleeve. At the same time, the left hand side of the servo cylinder is
emptied via the lower radial groove (port “c“) of the sleeve. Power steering fluid is led up
through the valve to the chamber above the spool and on back to the power steering fluid
reservoir.

When turning right.
The process is reversed. As long as the torsion bar is twisted, power steering fluid presses on
the rack so that servo effect is obtained. The difference between the valve spool and the sleeve
reduces when the power steering fluid actuates the rack in the same direction as the pinion.
When there is no longer a difference, the valve opens the passage returning power steering
fluid to the reservoir. Some power steering fluid continually circulates in the valve except when
the steering wheel is turned to an end position. This makes it possible for the control valve in
the power steering pump to work while circulation cools the power steering fluid.

MDPS
Motor Driven Power Steering(MDPS),
which is generally called Electrical
Power Steering(EPS), is developed
to assist a steering force by using
an electric motor without the help
of engine power. It controls motor
torque according to the steering
conditions resulting in optimal
steering characteristics and less
fuel consumption. Besides, it is an
environment friendly technology not
to use steering oil and is able to reduce
system weight as well as better

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service access owing to the removal of oil lines. Recently, EPS equipped cars are increasing
and EPS is expected to replace hydraulic power steering system. Electrical Power Steering is
divided into three types according to the motor location, Column type, Pinion type, Rack type.
Advantages
• Better fuel consumption: 2~3 %
• Environment friendly: Power steering oil & oil leak free
• Enhanced steering performance: Exact manipulation
- Basically the steering force is controlled depends on the vehicle speed.
- In addition to basic factor (vehicle speed), several logic such as damping control, friction
• control are adopted for optimizing steering ability.
- Required steering force is decreased in case of low vehicle speed for easy driving feeling.
- Required steering force is increased in case of high vehicle speed for safety.
• Weight reduction: by 2.4 Kg
• Driving performance: Engine power is not used for steering so vehicles acceleration
• performance will be improved.
• System status can be checked due to the communication with Hi-scan and warni lamp.
• NVH : Hydraulic noise may be eliminated and electrical motor has a function to absorb
the
• vibration from the steering column and it results the reduced vibration on steeri
wheel.